山东潍坊寒武系苗岭统乌溜阶馒头组上部的腕足动物

寒武系腕足动物属种多样性高、个体数量丰富、形态差异明显、地理分布广泛,具有辅助寒武系三叶虫生物地层划分和对比的潜力.华北板块寒武系苗岭统沉积和化石记录发育良好,是中国苗岭统的经典研究区之一.前人己针对华北寒武系苗岭统乌溜阶腕足动物的系统古生物学开展了一系列基础工作,但这些相关研究主要集中于辽宁地区,目前对华北其他地区苗...     

湖南零陵晚泥盆世叶虾类一新种——Echinocaris hunanensis sp. nov.

描述了湖南零陵普利桥晚泥盆世锡矿山组叶虾类一新种——Echinocaris hunanensis sp.nov..晚古生代叶虾类化石较为稀少,Echinocaris在亚洲是首次发现.     

An ecologically mixed brachiopod fauna from Changhsingian deep-water basin of South China: consequence of end-Permian global warming

The Late Permian Shaiwa Group of the Ziyun area of Guizhou, South China is a deep-water facies succession characterized by deep-water assemblages of pelagic radiolarians, foraminifers, bivalves, ammonoids and brachiopods. Here we report 20 brachiopod species in 18 genera from the uppermost Shaiwa Group. This brachiopod fauna is latest Changhsingian in age and dominated by productides. The palaeoecologic and taphonomic analysis reveals that the brachiopod fauna is preserved in situ. The attachment modes and substratum preference demonstrate that the Shaiwa brachiopod fauna comprises admixed elements of deep-water and shallow-water assemblages. The presence of the shallow-water brachiopods in the Shaiwa faunas indicates the involuntary settlement of shallow-water brachiopods. The stressed ecologic pressure, triggered by warming surface waters, restricted ecospace and short food sources, may have forced some shallow-water elements to move to hospitable deep-water settings and others to modify their habiting behaviours and exploit new ecospace in deep-water environments. We infer that the end-Permian global warming and subsequent transgression event may have accounted for the stressed environmental pressure in the shallow-water communities prior to the end-Permian mass extinction.     

Marine faunal assemblages in the Silurian-Devonian Keyser Limestone of the central Appalachians

Sedimentological analysis of the Keyser Limestone (Upper Silurian - Lower Devonian of the central Appalachians) indicates that its sediments were deposited in a range of marginal and shallow marine environments. Major depositional environments include: tidal flat, lagoon, barrier bar and island, and open marine shelf. Each major environment is represented by a lithofacies which is lithologically and faunally distinct. Tidal flat lithofacies are characterized by eurytopic organisms, including ostracodes, gastropods, stromatoporoids and blue-green algae. Lagoon lithofacies are dominated by bryozoans, brachiopods, ostracodes and stromatoporoids. Barrier lithofacies are characterized by rooted crinoids, encrusting bryozoans and robust brachiopods. Open shelf lithofacies contain a diverse fauna of cystoids, crinoids, bryozoans and brachiopods.
The distributions of faunal assemblages in the Keyser show no simple relationship to either water depth or distance from shore. They are, in general, related to the distributions of depositional environments.
Recurring associations of brachiopod genera were not found in the Keyser. With few exceptions, any genus may be found in any subtidal environment. Abundance of brachiopods is related to the abundance of local hard substrates (usually bryozoans).     

Survival patterns of macrobenthic marine assemblages during the end-Permian mass extinction in the western Tethys (Dolomites, Italy)

The ecological competition between brachiopods and bivalves is analysed by means of a quantitative palaeoecologic method applied on four assemblages located within a short stratigraphic interval, approximately 2 m thick, in the lower Tesero Member of the Werfen Formation (in the Southern Alps). The assemblages originate from the Tesero, Bulla and Sass de Putia sections. The analysed stratigraphic interval, uppermost Changhsingian in age, is located between the early and heaviest phase of the end-Permian mass extinction, which occurred across the Bellerophon/Werfen formational boundary (Event Boundary), and the Permian/Triassic boundary (Chronological Boundary), when nearly all the Permian stenotopic holdovers disappeared.These assemblages are characterised by small sized skeletons (“Lilliput effect”), which represent an adaptive survival strategy in stressed and harsh habitats resulting from the climatic and palaeoceanographic changes connected with the mass extinction. The Tesero assemblages are dominated by rhynchonelliform brachiopod Orbicoelia (bed CNT10) or Streptorhynchus (bed CNT11A), which were mostly attached at the top of shallow microbialitic mounds. These assemblages are again dominated by Permian stenotopic taxa and show a Palaeozoic structure. The Tesero habitat, which again permitted the survival of brachiopods, represented one of the last refuges in the western Tethys. On the contrary, the Bulla (BU9-10) and Sass de Putia (wPK13A) assemblages are bivalve-dominated, and thus show an ecologic structure typical of Early Triassic post-extinction marine benthic communities or Palaeozoic stressed marine communities. The bivalve-dominated assemblages proliferated in prevailing muddy siliciclastic substrates, with brief episodes of microbial algal growth. The most important environmental limiting factors and leading causes of end-Permian mass extinction are discussed in terms of palaeoautecologic and palaeosynecologic analysis.The different taxonomic composition and ecologic structure of the assemblages is related to palaeogeography, including water depth and connections with the open sea. The brachiopod-dominated assemblage, exclusive of the Tesero section, proliferated in microbial carbonate habitats in near-shore environments. The bivalve-dominated assemblages, which were more widespread than the brachiopod assemblages in the Dolomites and also occurred in other western Tethys localities, occur in more open and deeper marine environments. In the western Tethys margins, the local distribution of mixed faunas suggests that the extinction of Permian stenotopic taxa was caused by the onset of poisonous water on the shelves originating from deep marine environments.This extinction pattern appears to be a regional phenomenon and does not seem be applicable on a global scale. The extinction events were controlled by a complex network of interactive factors and the survival of faunal elements was probably stochastic.     

Bouchardia rosea,a vanishing brachiopod species of the Brazilian platform: taphonomy,historical ecology and conservation paleobiology

Dead-live faunal comparisons can offer powerful data to detect natural or human-induced population changes in the late Holocene. Here, we document dead–live comparisons for death assemblages of the brachiopod Bouchardia rosea in nearshore (0–45 m) environments along the northern coast of São Paulo State, Brazil. The sampling programme included 30 stations (14 at Ubatuba, 16 at Picinguaba bay). The bottom was sampled via Van Veen grab sampler, and also dredged. Out of 30 stations, 22 yielded brachiopods. The fidelity estimates were obtained by direct comparisons of live biota with dead shells. A total of 6627 brachiopods were recovered, 5339 (80.6%) from Ubatuba and 1288 (19.4%) from Picinguaba. Out of these, 6621 (99.9%) were empty, dead shells, while only six individuals (0.1%) were found alive, all in the Picinguaba Bay. These results suggest extremely poor dead–live compositional fidelity for B. rosea assemblages. The spatial data suggest that the distribution of B. rosea accumulations has been highly patchy in the region, whereas the great scarcity of live brachiopods may point to a recent decline in local populations. Several lines of evidences indicate that changes in water temperature, nutrient availability, population history and even pollution, may have all affected spatio-temporal dynamics of B. rosea populations.     

Brachiopodes toarciens de la coupe d’Aït Athmane,Haut Atlas centro-oriental (Maroc)

The Aït Athmane section is located in the eastern part of the central High Atlas, about 20 km north of Errachidia. Its Toarcian series consists of silty marl and silty marly limestone. Its lower part, of early (Levisoni Zone?) to middle Toarcian (Bifrons and Gradata? Zones) age, is rich in brachiopods (rhynchonellides and terebratulides). Its upper part, of late Toarcian age, is rich in terebratulids. Among eighteen reported brachiopod taxa, six are new for the central High Atlas. Their specific assemblages and stratigraphic distributions are similar to those of the Toarcian brachiopods reported from several basins of northern and southern margins of the Tethys and the Subboreal domain, particularly of western France.     

Biogeography of the recent brachiopods

The vertical, latitudinal, and circumcontinental zonality of the distribution of the species, genera, and families of recent brachiopods is considered. The distortions of the latitudinal and meridional symmetry of the biogeographic structure of the ocean are analyzed in view of the patterns of the global circulation of the surface and intermediate waters. Thus ancient faunas may be reconstructed based on data on the structural characteristics of the taxocene of recent brachiopods. The features of the paedomorphic evolution of brachiopods from the different families in extreme habitats (interstitial, underwater caverns, submarine rises, abyssal depths, hydrothermal areas, and margins of habitats) are discussed. The biogeographic structure of bottom dwellers is shown to simplify with depth as well as with simplification of the hydrological structure of the ocean. The important role of the bathyal oceanic zone (slopes of continents, islands, submarine mountains, ridges, and rises) in the preservation of faunal relicts is shown. The historical change from brachiopods to bivalves that occurred from the Paleozoic to the Mesozoic and Cenozoic is shown to have resulted not from competitive exclusion, but from complex and global changes in the plankton composition, which were unfavorable for articulate brachiopods, which had already developed specialized feeding habits, feeding on food that led to the production of almost no metabolic waste products; they had even partly lost their alimentary canal. The development of shelly plankton and, especially, of diatoms hampered the post-Paleozoic revival of large assemblages of articulate brachiopods in shallow-water habitats. The unfilled ecological niches were colonized by bivalves, which were widely adapted to feeding on live phyto-and zooplankton. Recent articulate brachiopods, which are adapted to feeding on the products of decay of dead plankton, form a belt of densely populated settlements of the organic biofilter outside the photic zone on the seaward edge of shelves and on the upper parts of the slopes of continents, islands, and submarine rises throughout the world.     

Paleobiogeography of Mesozoic brachiopod faunas from Andean–Patagonian areas in a global context

During the Mesozoic, the Andean region has played a hinging role between high- and low-latitude faunas, which are, respectively, characterized by stocks that display long-term fidelity. This paper is aimed at providing an updated review of Late Triassic to Late Cretaceous South American articulated brachiopods in the light of previous knowledge at worldwide scale. Late Triassic brachiopods from the Argentine–Chilean Andes show unmistakable Maorian (or Notal) faunal elements alongside some more cosmopolitan genera, with certain influence of Eastern Pacific taxa. By Early Jurassic times, differentiation of Tethyan and Boreal Realms became progressively evident in Europe. In South America, Hettangian–Sinemurian brachiopod faunules from the Argentinian Andes are somewhat impoverished, with mostly cosmopolitan genera showing certain affinities to Maorian species, and with the addition of some endemics later. Increasingly, diverse Pliensbachian Andean brachiopods denote close relationships to Celto-Swabian taxa, then by Domerian times, a certain degree of endemism was developed, though somewhat delayed Tethyan influences, and persistent links with New Zealand are subordinately recognizable, too; most Toarcian assemblages reveal basically Celto-Swabian and Iberian affinities as well. East-west austral links across the Pacific may have been favored by migratory routes fringing the Gondwana margin, whereas faunal exchange with the western end of the Tethys appears to reflect an intermittent shallow-marine connection through the Hispanic Corridor. During the Middle Jurassic, distinction of Tethyan and Boreal Realms was maintained in the northern Hemisphere, and the differentiation of an Ethiopian or Southern Tethyan fauna became better characterized. Aalenian and Bajocian brachiopods of the Andes display generic affinities mainly with those from western Europe, with some minor endemic developments; brachiopods recorded from the Bathonian–Callovian of Argentina (and Chile) also occur along the northern Tethyan margin, yet with some genera extending into Indo-Ethiopian areas. During the Late Jurassic, Boreal faunas from high-latitudes became even more strongly differentiated from low-latitude, Tethyan ones. Oxfordian and Tithonian brachiopods from the Andes apparently belong to genera of cosmopolitan or northern Tethyan affiliation, yet there are few elements in common with other eastern Pacific areas, such as Mexico. Early Cretaceous brachiopods, in addition to Andean basins of Chile and western Argentina, are known also from Patagonia and Tierra del Fuego. They belong mostly to widely distributed, mainly Tethyan genera, with some quasi-cosmopolitan and circum-Pacific components (some shared with Antarctica become noticeable). Late Cretaceous brachiopods from northern Patagonia show significant affinities to Maastrichtian ones of northwest Europe and central Asia, which calls for further assessing the potential role that may have played the trans-Saharan passageway in such dispersal. Broad aspects of Mesozoic brachiopod paleobiogeography are fairly well understood, yet details of ranking and naming of certain units are still in need of more agreement.     

贵州剑河寒武纪凯里生物群中拟轮盘水母钵(Pararotadiscus)和腕足类共存现象的初步研究

贵州剑河革东寒武纪凯里生物群中水母状化石属种单调,仅发现1属1种贵州拟轮盘水母钵Pararotadiscus guizhouensis(Zhao et Zhu,1994),但却有丰富的生态现象.近40%的标本与腕足类、三叶虫、金臂虫、棘皮动物或遗迹化石Gnrdia共存,是目前全球水母状化石中罕见的丰富生态现象.其中65件贵州拟轮盘水母钵盘体上、下或周围出现了背、腹壳分散保存的腕足类,说明腕足类与贵州拟轮盘水母钵共同埋藏;1块标本的丛状触手中还包裹有腕足类,说明丛状触手不是类似于植物根系的固着器.这种现象还证实贵州拟轮盘水母钵不是固着而是浮游生活的,其与腕足类壳瓣共存,主要是浮游的贵州拟轮盘水母钵死亡后沉落海底与腕足类壳瓣重叠的结果.     

Latitudinal and depth gradients in marine predation pressure

Aim There is a general paradigm that marine predation pressure increases towards the tropics and decreases with depth. However, data demonstrating global trends are generally lacking. Rhynchonelliform brachiopods inhabit all the oceans and often survive shell‐crushing predator attacks. We investigate shell repair in brachiopods across a range of Southern Hemisphere and tropical Northern Hemisphere latitudes and depths. Location The Southern Hemisphere and tropical Northern Hemisphere. Methods We analysed the frequency of shell repair in 112 bulk samples, over 70% of which showed traces of shell damage and repair. Results The pattern of shell repair frequency (RF) was more complicated than the anticipated increase with decreasing latitude, with low levels at both polar and tropical sites but high levels at temperate latitudes. This pattern is only evident, however, in shallow water assemblages; and there is no latitudinal trend in water depths greater than 200 m, where shell RF is systematically low. There was a significant logarithmic relationship between RF and depth. Low polar repair rates reflect reduced predation pressure, directly supporting the global paradigm. Low rates in the tropics appears counter to the paradigm. However, tropical brachiopods are generally very small (micromorphic) in shallow water and below the minimum size at which damage is recorded anywhere. Main conclusions Predation pressure decreased logarithmically with depth. At shallow depths (< 200 m) RF showed its highest levels in the mid temperate latitudes with decreasing frequency towards both the tropics and the poles. Low levels of shell repair at high latitudes are likely to be due to a lack of crushing predators, but in the tropics it is suggested that the low frequency is a result of the small size of tropical brachiopods. We hypothesize that micromorphy in this region may be an outcome of high predation pressure.     

Succession and replacement in the development of Silurian brachiopod populations

Fluctuating water depths in platform seas covering central North America during late Llandovery time introduced shifts in the spectrum of coral-algal, pentameran, and stricklandian communities. Opportunistic orthotetacean brachiopods were common during these times of community replacement. A pavement constructed by their flat shells was sometimes used as the initial substrate for attachment by the spat of pentameran brachiopods. Both orthotetacean and pentameran shells served as the initial substrate for stricklandian brachiopods. With the decline of a pentameran or stricklandian population, disarticulated shells provided a substrate for repopulation. An assemblage of immature Pentamerus in life position indicates that the typical umbo-down posture was an early result of maximum packing. Development of more advantageously placed individuals severely restricted the growth of others trapped between the substrate and the beak regions of surrounding neighbors. After pentameran assemblages were buried in life position, scouring of the sea bottom frequently produced erosion surfaces which truncated their thin shells. These surfaces were sometimes penetrated by boring organisms, and were firm enough for brachiopod repopulation.     

Brachiopods from cryptic coral reef habitats in the northern Red Sea

In contrast to the Palaeozoic to Jurassic fossil record, modern tropical and subtropical shallow-water brachiopods are typically small-sized and mostly restricted to cryptic habitats in coral reefs, but information on microhabitat-composition is scant. At Dahab, northern Red Sea, living brachiopods of the genus Argyrotheca were only detected on massively encrusted coral colonies attached to encrusting foraminifers and coralline red algae. Three samples from autochthonous sediments underneath coral colonies are comparatively rich in the brachiopod genera Megerlia and Argyrotheca, and additionally show low numbers of Novocrania and Thecidellina. Based on a coarse-grain analysis including more than 16,000 components >1 mm, these brachiopod shells co-occur with skeletal components of 11 higher taxa. Decapods, fixosessile foraminifers, molluscs, scleractinians, and coralline red algae clearly dominate the assemblages. Brachiopods in this study always contribute less than 2% to the sediment composition. This confirms previous results that even in brachiopod habitats the contribution of brachiopod shells to the total sediment composition is almost negligible. Our study indicates that brachiopods co-occur with pteriomorph bivalves and other epifauna in the cryptic habitats with limited space for encrusters or epibionts on the undersides of scleractinians and it tentatively supports the hypothesis of brachiopods preferring habitats with low grazing pressure, because shelly components of grazers (polyplacophorans and regular echinoids) are rare in our samples.     

Size-frequency and population structure of brachiopods

The living terebratulids, Terabratulina unguicula, Terebratalia transversa, Laqueus vancouverensis, and the rhynchonelid Hemithiris psittacea were studied in the San Juan Islands, Washington, U.S.A. Those results and a review of a the literature lead to the conclusion that most brachiopod populations experience episodic recruitment at intervals which may be irregular. The occurrence of juveniles attached to adults, brooding, and bi- or multimodal size-frequency distributions demonstrate that, contrary to a previously suggested hypothesis, adult brachiopods do not generally exclude juveniles from the same area. The commony observed rarity of small individuals is regarded as a product of local recruitment failure due to patchy distribution of larvae; it does not justify the assumption that brachiopods are unaffected by high post-larval juvenile mortality. However, the frequent rarity of small individuals confirms that this cannot be used as a criterion of transport in assemblages of fossil brachiopods.     

Microfacies and depositional environment of an Upper Triassic intra-platform carbonate basin: the Fatric Unit of the West Carpathians (Slovakia)

Facies associations of the Rhaetian Fatra Formation from the Veká Fatra Mts. (West Carpathians) were deposited in a storm-dominated, shallow, intra-platform basin with dominant carbonate deposition and variable onshore peritidal and subtidal deposits, with 21 microfacies types supported by a cluster analysis. The deposits are formed by bivalves, gastropods, brachiopods, echinoderms, corals, foraminifers and red algae, ooids, intraclasts and peloids. A typical feature is the considerable variation in horizontal direction. The relative abundance and state of preservation of components as well as the fabric and geometric criteria of deposits can be correlated with depth/water energy-related environmental gradients. Four facies associations corresponding to four types of depositional settings were distinguished: a) peritidal, b) shoreface, above fair-weather wave base (FWWB), c) shallow subtidal, above normal storm wave base and d) above maximum storm wave base. The depositional environment can be characterized as a mosaic of low-relief peritidal flats and islands, shoreface banks and bars, and shallow subtidal depressions. The distribution and preservation of components were mainly controlled by the position of base level (FWWB), storm activity and differences in carbonate production between settings. Poorly or moderately diverse level-bottom macrobenthic assemblages are dominated by molluscs and brachiopods. The main site of patch-reef/biostrome carbonate production was located below the fair-weather wave base. Patch-reef/biostrome assemblages are poorly diverse and dominated by the branched scleractinian coral Retiophyllia, forming locally dm-scale autochthonous aggregations or more commonly parautochthonous assemblages with evidence of storm-reworking and substantial bioerosion by microborings and boring bivalves.Facies types and assemblages are comparable in some aspects to those known from the Upper Triassic of the Eastern and Southern Alps (Hochalm member of the Kössen Formation or Calcare di Zu Formation), pointing to similar intra-platform depositional conditions. The absence of large-scale patch-reefs and poor diversity of level-bottom and patch-reef/biostrome assemblages with abundance of eurytopic taxa indicate high-stress/unstable ecological conditions and more restricted position of the Fatric intra-platform setting from the open ocean than the intra-platform habitats in the Eastern or Southern Alps.     

A spinose stem group brachiopod with pedicle from the Middle Cambrian Burgess Shale

A new genus and species of a Middle Cambrian stem group brachiopod, Acanthotretella spinosa n. gen. and n. sp., is described from the Burgess Shale Formation. Most of the 42 specimens studied came from the Greater Phyllopod bed (Walcott Quarry) and were collected from five bed assemblages, each representing a single obrution event. Specimens are probably preserved within their original habitat. In contrast to all brachiopods known from the Burgess Shale, the shells of the new stem group brachiopod are often deformed and do not show signs of brittle breakage, which suggests that the valves were originally either entirely organic in composition or, more likely, had just a minor mineral component. Acanthotretella spinosa differs from all the other described Cambrian brachiopods in that it is covered by long, slender and possibly partly mineralized spines that are posteriorly inclined at an oblique angle away from the anterior margin. The spines penetrate the shell and are mainly comparable with the thorn‐like organic objects that have been inferred from early siphonotretoid brachiopods. The pedicle was slender and was composed of a central coelomic region and emerged from an apical foramen at the end of an internal pedicle tube. The finding of a pedicle attached to the macrobenthic algae Dictyophycus and other epibenthos implies that A. spinosa did not have an infaunal mode of life. The visceral region and interior characters are poorly preserved.     

Studies of fossil brachiopods of Mongolia: Ordovician,Silurian, Devonian,Carboniferous, and Permian

Fossil brachiopods from the Ordovician, Silurian, Devonian, Carboniferous, and Permian deposits of Mongolia have been studied for the last forty-five years by the Joint Soviet-Mongolian (later RussianMongolian) Paleontological and Geological Expeditions. New data on the taxonomic composition, stratigraphic and geographic distribution of the brachiopod assemblages have been obtained. The brachiopod systematics has been further refined and detailed, and the stratigraphic and correlation scales and biogeographic reconstructions have been elaborated for the Paleozoic of Mongolia.     

New paleobiogeographical and paleoenvironmental insight through the Tortonian brachiopod and ichnofauna assemblages from the Mediterranean-Atlantic seaway (Guadix Basin,SE Spain)

The paleogeography of the Late Neogene Atlantic-Mediterranean seaway via the Betic-Rifean Domain is quite complex due to the presence of several marine corridors. The study of transitional basins in these seaways is crucial to understand the configuration and evolution of the Mediterranean-Atlantic inter-connection. A mixed skeletal-siliciclastic sandstone succession located in one of these transitional areas (Guadix Basin, Southern Spain) was studied from a comprehensive paleontological standpoint focused on the main benthic assemblages (foraminifera, brachiopods, and trace fossils), integrating the data with the study of planktic foraminifera for an accurate biostratigraphic framework. Brachiopods are mostly represented by the Aphelesia-Gryphus assemblage. Two trace fossil assemblages were observed, dominated by Ophiomorpha with Bichordites (1) and Macaronichnus (2), respectively. The benthic foraminiferal assemblage is mostly represented by Planulina and Cibicides. The data gathered from the benthic communities reveal habitats with high-energy and turbulent conditions in an outer neritic-upper bathyal bathymetric range. Brachiopods from the Alicún section show a Mediterranean paleobiogeographic affinity. They were constrained in the Late Tortonian to the restricted basins of the Betic-Rifean Seaway and after the Messinian Salinity Crisis proliferated in both Mediterranean- and Atlantic-type basins of the Betic-Rifean Domain. The Guadix Basin contributed to the Mediterranean-Atlantic faunal inter-connection through the Betic-Rifean Seaway during the Late Tortonian and facilitated the earliest Pliocene expansion of brachiopods in the Mediterranean.     

Linking taphonomy to community-level abundance: Insights into compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps)

Although actualistic live/dead comparisons lead to robust estimates of fidelity of modern death assemblages, quantitative evaluation of fidelity of fossil assemblage remains uncertain. In this paper, effects of storm reworking on compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps, Austria) are evaluated. An exploratory approach is based on comparison of reworked and non-reworked assemblages in ordination analyses. Non-reworked assemblages of one or more communities provide a baseline for evaluation of fidelity of reworked assemblages. In siliciclastic-rich intervals of the Kössen Formation, shell concentrations are represented by (1) packstones with small, shallow infaunal bivalves, (2) floatstones and pavements with large semi-infaunal bivalves, and (3) bioclastic marlstones. In carbonate-rich intervals, bioclastic floatstones with bivalves and brachiopods occur. Analyzing all shell concentrations, eight sample groups sharing similar species composition are discriminated. Limited effect of storm reworking on composition of shell concentrations is indicated by (1) a general persistence of six sample groups when only non-reworked assemblages are analyzed, (2) similarity in composition between reworked and non-reworked assemblages within sample groups, and (3) compositional segregation between non-reworked assemblages of distinctive sample groups, mostly without any reworked assemblages of intermediate composition.Depth-related variations in dead-shell production, shell destruction and body size governed preservation and distribution of the shell concentrations along onshore-offshore gradient in the Kössen Basin. First, at times when environmental conditions were unfavorable for shell producers, coupled with high background shell destruction rates, limestone beds formed during storm events were shell-poor. Second, less common shell concentrations in upper than in lower parts of siliciclastic intervals can be related to higher environmental stress in shallower habitats. Third, the difference between shell concentrations dominated by small and large bivalves is driven by between-habitat differences in body size and is not due to a differential sorting of small and large shells. Combining community analysis based on species abundances with taphonomic analysis can thus be helpful in tracking fidelity of fossil assemblages.     

ORDOVICIAN (ARENIG–CARADOC) SYNTROPHIIDINE BRACHIOPODS FROM THE EAST BALTIC REGION

Abstract:  Syntrophiidine brachiopods are a rare and poorly known component of Ordovician Baltoscandian faunas. They appear in the East Baltic in the Billingenian (lower Arenig) as part of the earliest known benthic assemblages dominated by elements of the Palaeozoic Evolutionary Fauna. These faunal assemblages usually include bryozoans, ostracodes, and the earliest known porambonitoids, strophomenides and endopunctate orthides, such as Idiostrophia and Orthidium , which later became characteristic of the Whiterockian brachiopod assemblages in Laurentia, but by that time had disappeared from Baltica. The superfamily Syntrophioidea reappears in Baltoscandia in the mid Caradoc. In contrast, Porambonitoidea remained the integral part of the Baltoscandian brachiopod associations through the Ordovician. Porambonites , herein redefined on the basis of restudy of the type species P. intermedius , includes only smooth porambonitoids; taxa with the distinctive ornament of radiating rows of pits first appeared in the group in the mid Arenig. The taxa Eoporambonites gen. nov., Tetralobula peregrina sp. nov., Idiostrophia prima sp. nov. and Idiostrophia tenuicostata sp. nov. are erected.